This invention relates in general to the field of visual displays, and more particularly to a method for selective deposition of an emissive layer in electroluminescent displays.
Flat screen displays are provided by light blocking, reflecting technologies, and light emitting technologies. One type of light blocking flat screen display is a liquid crystal display (LCD). LCDs are based on blocking light from a separate light source behind an LCD panel. One type of light emitting flat screen display is based on light emitting diodes (LEDs). Since light emitting displays generate light, a separate light source is not used.
Light emitting displays include cathode ray tube (CRT), plasma discharge, thin film electroluminescent, and light emitting diode (LED) based architectures. The LED""s can be either discrete inorganic (i.e., III-V or II-VI compound semiconductor devices) or thin film organic diodes. Thin films of organic compounds offer the potential to realize optoelectronic devices with properties unattainable with conventional semiconductor materials. Organic electroluminescent devices are of considerable interest in various display applications because of their high efficiency and variation in colors. Using multilayer structures, emitting layers, transport and luminescent materials, including polymers, and efficient injection contacts, these organic-based devices can be operated with a DC voltage as low as a few volts and provide luminous efficiencies greater than 1 lm/W over a wide spectral range, making possible the fabrication of a full-color display panel.
Organic light emitting material recombines a hole and an electron thereby creating a photon of energy in the form of visible light. Since color displays require a combination of colors, the organic materials used in light emitting displays need to be organized and patterned to provide a color element for each pixel. Conventional patterning techniques such as photoresist techniques are not applicable to patterning organic materials since the solvent used in photoresist techniques cannot distinguish between the resist material and the organic material.
One method of patterning organic materials is the use of a shadow mask. The use of shadow masks includes building vertical columns and depositing the organic material on a substrate from an angle. Since the material is deposited at an angle, each vertical column creates a shadow area behind the column that does not receive the deposited material. Although this method has been used for integrated circuit fabrication, the use of this method for large flat screen light emitting displays is impractical since the vertical columns would lose stability as height increases. In flat screen displays, the larger the display, the larger the pixel. Since multiple colors are necessary to create a color display, multiple shadow masks and several fabrication steps are needed. Using multiple shadow masks slows down the processing time and increases the cost of the devices.
In accordance with the present invention, an improved method for selective deposition of an emissive layer in electroluminescent displays is provided that substantially eliminates or reduces disadvantages and problems associated with conventional fabrication techniques.
According to an embodiment of the present invention, there is provided a method for forming an emissive layer for an electroluminescent display that includes positioning a substrate in spaced relation to a port of a microeffusion cell and transporting the substrate across the port at a substantially constant rate. The method then provides for effusing an emissive material from the port and adhering at least a portion of the emissive material effused from the port to a defined region of the substrate to form an emissive strip having a substantially constant width on the substrate.
The present invention provides various technical advantages over conventional fabrication techniques for light emitting displays. One technical advantage is that the present invention provides a continuous process for fabricating flat panel displays. In particular, emissive and other layers are continuously formed. Another technical advantage is that by using selective deposition for the emissive layer, any patterning steps are eliminated. This leads to reduced fabrication time and fewer fabrication processing steps. Another technical advantage is that manufacturing costs are reduced as compared to using fabrication techniques such as shadow masking. Other technical advantages may be readily apparent to one skilled in the art from the following figures, description, and claims.